ML24348A085
| ML24348A085 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 12/13/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24348A006 | List:
|
| References | |
| LO-176318 | |
| Download: ML24348A085 (1) | |
Text
Response to NuScale Topical Report Audit Question Question Number: A-NonLOCA.LTR-62 Receipt Date: 06/28/2024 Question:
TR Section 6.1.3 states: (( 2(a),(c) Please provide proposed markups to the TR.
Response
The purpose of the hot channel heat structure described in TR-0516-49416-P, Revision 4, Non-Loss-of-Coolant Accident Analysis Methodology, Section 6.1.3 is to allow critical heat flux (CHF) to be calculated in NRELAP5. ((
}}2(a),(c)
NuScale Nonproprietary NuScale Nonproprietary
Table 1: (( }}2(a),(c) (( }}2(a),(c) ((
}}2(a),(c)
NuScale Nonproprietary NuScale Nonproprietary
TR-0516-49416-P, Revision 4, Section 6.1.3 is revised as indicated in the attached markups to ((
}}2(a),(c) consistent with the response above.
((
}}2(a),(c)
Markups of the affected changes, as described in the response, are provided below: NuScale Nonproprietary NuScale Nonproprietary
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 494 6.1.2 Core Kinetics The separable point kinetics model is used to calculate reactivity feedback to the core power from the moderator, the fuel, and decay heat. The various point kinetic parameters are input based on the fuel burnup (for example, new core, BOC, or EOC) and control rod insertion amounts assumed for the analysis. NRELAP5 assumes an infinite core operating time at the initialized power when determining the decay heat power. The fission product decay type is specified as 'gamma-ac' with the 'ans73' model, which calculates decay heat in accordance with the 1973 ANS standard while adding the contribution from actinides. A fission product yield factor of 1.0 is specified in the base models, which can be changed to suit the scenario being analyzed. Control variable inputs to the core kinetics model are used to simulate control rod movement and reactivity feedback from a variety of parameters including, but not limited to fuel temperature, moderator temperature, and moderator density. Trips are used to enable or disable each reactivity feedback mechanism as needed. The fuel and moderator feedback controllers utilize volume weighting of the fuel and moderator temperatures to specify bounding reactivity feedback input; volume weighting is used for consistency with how the reactivity feedback design limits are confirmed in the core design. A scram table is used to simulate control rod insertion following reactor trip. Appropriately conservative scram curves are developed based on the core time-in-life, the initial power level, the location of the control bank, and other relevant factors to preserve the minimum shutdown margin. 6.1.3 Fuel Rod Design Input (( the fuel/pellet region, one interval for the gas gap and }}2(a),(c) Fuel performance data (Section 4.3.1.2) is incorporated into the NRELAP5 non-LOCA model via material thermal property tables for the UO2 fuel region, the gas gap, and the cladding. Because the density of UO2 changes with burnup, the thermal property tables can be revised as needed to match time in cycle. Audit Question A-NonLOCA.LTR-62 As discussed in Section 4.3.1.1, the core power distribution is based on a nominal average axial power shape with power distributed solely in the fuel pellet. (( }}2(a),(c)
Non-Loss-of-Coolant Accident Analysis Methodology TR-0516-49416-NP Draft Revision 5 © Copyright 2024 by NuScale Power, LLC 495 (( }}2(a),(c) The gap thermal conductivity is calculated at bounding values burnup to ensure that the fuel volume average temperature is appropriately bounded compared to fuel performance design data. This bounding method also accounts for gap closure over the fuel cycle. 6.1.4 Secondary System 6.1.4.1 Feedwater System In an NPM design two feedwater lines penetrate the CNV immediately downstream of the FWIVs. Each feedwater line splits into two lines before connecting to the SGs. (( Audit Question A-NonLOCA.LTR-63 Audit Question A-NonLOCA.LTR-63 }}2(a),(c)}}